At present, radio communication systems such as cellular phone systems or wireless local area networks (wireless LANs) are widely used. In the standards body for radio communications, a lively discussion about the next-generation radio communication standards has been performed to further improve a communication speed and communication capacity. For example, in the 3rd generation partnership project (3GPP), a discussion is held regarding the radio communication standards referred to as so-called long term evolution (LTE) or long term evolution-advanced (LTE-A).
In such a radio communication system, a wider bandwidth of a frequency band used for the radio communication system is promoted. Further, some radio communication systems perform a communication (multiband communication) using a plurality of frequency bands. For example, a wide frequency band of 600 MHz to 6 GHz is possibly used in the next-generation radio communication standards. In this case, the radio communication apparatus adapted to the standards includes an antenna adaptable for the above-described wide frequency band. On the other hand, miniaturization and weight saving may be demanded for a portable radio communication apparatus such as a cellular phone.
For an antenna used for the radio communication, there is proposed a gate antenna device that suppresses power consumption or leakage electric fields, expands a communication range with an IC-integrated medium, and improves communication accuracy. This gate antenna device has a power-fed loop antenna to which a signal current is supplied and a non-power-fed loop antenna to which a signal current is not supplied (e.g., Japanese Laid-open Patent Publication No. 2005-102101).
Further, there is proposed a radio frequency identification (RFID) tag reading system capable of easily setting a shape of a reading area where an RFID tag is readable. This RFID tag reading system includes a first antenna that is connected to a reading device via a feeding wire, a second antenna that is located rightly in the radiation direction of the first antenna, and a third antenna that is connected to the second antenna via a feeding wire (e.g., Japanese Laid-open Patent Publication No. 2008-123231).
Further, the applicant performs an application for a patent (Japanese Patent Application No. 2009-82770) about an antenna capable of adjusting an operating frequency in combination of a monopole antenna and a loop antenna. However, the antenna described in this application for a patent can stand improvement about the tuning of an operating frequency, particularly, the tuning of a low frequency side. A circuit for a portion in which an electric loop is formed makes easy the tuning of a high frequency side and also, preferably makes easy the tuning of a low frequency side with respect to a desired operating frequency.